Cathode arrangement for braun tubes



March 3 K. SCHLESING ER GATHODE ARRANGEMENTYFOR BRAUN mass a as Filed May 13, 1933 Fig.5

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Patented Mar. 5, 1935 I CATHODE ARRANGEMENT FOR I TUBES FICE BRAUN Kiirt Schlesinger, Germany Application May 13, 1933, Serial No. 670,818

e In Germany May 14, 1932 17. Claims. (01. arc- 21.5)

The subject matter of the in'yention'is a Braun tube having a cathode of a particularly durable kind and large yield of current.-

According to the nvention, the cathodeis arranged in. a double-walled, hollow cylinder, the

-' charge.

, result at all within low that the same is outer wall of which is constituted by a closed metallic cylinder, and the inner wall of which consists of alarge-mesh grid. The two end walls of the cylinder preferably consist of circular metallic rings. nected together by welding. According to the invention, there may be employed, a bifilar cathode, which is placed about the grid forming the inner wall, preferably at" a slight distance from the same. As cathode there is employed either an ordinary oxide cathode or a cathode produced according to the metallic vapour process, or also an alloyed cathode. The cylinder-in the case of oscillograph tubes-is fur-n nished with a slight positive potential as compared with the cathode, so that within the cylinder there is'a space which is free of space If the tube is to be employed for television purposes, the control potential may be applied between the grid and the cathode, so that the control of the intensity takes place by the space charge control.

The electrons proceeding from the cathode first enter the inner space of the inner grid cylinder, and are withdrawn from this space, which is free of space charge, in the direction of the anode by the field effect of the anode.

Since in accordance with the invention the positive bias of the cylinder'is made'to be so situated below the ionization potential of the gas filling, ions are unable to the cathode cylinder. The ,ions proceeding from the anode .fly through the grid cylinder in the direction indicated by the arrow. By reason of the arrangement according to the invention the cathode is, therefore, reliably protected against the so-called drumming effect. At the same time any rear or lateral emission is safely avoided by means of the arrangement according to the invention.

According toa further embodiment of the invention, the cathode may be constructed as an indirectly heated cathode. The single elements may be constructed in such fashion that the same, upon the assembly, centre each other, so that subsequent centring is not required.

According to a further object of the invention, the cathode-arrangement may possess the form of. a discharge stretch comprising a preferably hot cathode, and possibly grid and anode, which stretch is preferably disposed in such fashion that the direction of the electrons within this discharge stretch is situated vertically to the axis of the tube.

The single parts may be con tested against the impact of The electrons forming the cathode ray are, in accordance with the invention, sucked out from this primary path of electrons by the suctional action of the high-potential anode of the Braun tube, possibly with the intermediate connection of a. shutter and also suitable concentration means.

Since the number of electrons passing into the primary path may be controlled in wattless fash ion by the application of suitable potentials to the grid, and since furthermore the speed of the electrons along the primary path always remains constantindependently of their number,

there is rendered possible in this manner the generation of a wattless-controllable cathode,

ray, in which the position of the image point on the screen is not affected by the intensity of the ray. 1 v

The arrangement according to the invention is illustrated by way ofexample in the drawing, in which Fig. 1 shows the arrangement in section, whilst in Fig. 2 there is shown the grid cylinder, andin Fig: 3 the arrangement having an after-connected preliminary concentration and focussing arrangement.

Fig. 4 is a section through the arrangement according to the invention, whilst in Fig. 5 on a. largerscale a detail of Fig. 4 is shown. 4

Fig. 6 is an arrangement, in which the cathode is constructed in the form of a cylindrical path of discharge, wherein the anode is made in annular form and concentrically surrounds the cathode ray to be produced, whilst in Fig. 7 there is illustrated an arrangement by way of example employing an electron path consisting of a desired three-electrode system.

In the Figures 1-3, 1 is the double-walled hollow cylinder having the double-wound hot cathode 2 and its current leads 3 and 4, 12 is the irm'er grid cylinder, and 5 and 6 are small plates, which consist for example of alkaline earth metal, and which for the purpose of producing metallic vapour cathodes and for improving the vacuum may be atomized either by eddy current heating or by means of the filament 7 and 8. By means of the arrows there is indicated on the one hand the direction of the electrons and on the other hand the direction of the ions. As

- shown by the drawing, the ions fly substantially in a straight direction through the cylinder, so that the cathode itself is completely proions.

As shown by Fig. 3, there may be arranged in front of the end wall of the cathode cylinder a member formed in the manner of a'hollow re 'fiector, by means of which member, when the same possesses a correspondingly selected potential in relation to the "ray, a preliminary conly possess the same potential as the cathode centration takes place of the rays emerging from the opening in the cathode cylinder.

The applicant has found that this potential preferably may be made positive in relation to the cathode, but weakly negative as compared with the ray. If the front end wall of the cathode cylinder is-constructed itself in the form of a hollow reflector, the'same may convenientcylinder.

However, particularly for television purposes, it is desirable to construct this hollow-reflector shutter according to the invention separately, and

electrons. Since the form of the field would ap- I pear to be substantially settled by the hollow reflector shutter in the vicinity of the cathode, the

- potential of the Wehnelt cylinder of the electron- I borings (for example six).

optical system is no longer of the same critical kind. The aperture of the electron-optical system is also considerably increased by the series connection of the hollow reflector shutter according to the invention. Owing to the reduced sensitiveness it is quite readily possible to exchange differ nt tubes.

Na urally in Fig. 3 the hollow reflector shutter is merely shown diagrammatically and by way of example. The form and the dimensions of the shutter and also the spacing of the same from the electron-optical system may-be determined on each occasion without difilculty by simple experiment. It is essential in each case that the hollow reflector-like shutter possesses in relation to the ray a suitable negative potential which is not too high. The potential of the shutter is accordingly also dependent on its spacing from the anode and ghedcathode, i. e., on its arrangement within the e In the Figures 4 and 5,1 and 10 are two insulating tubes, composed for example of porcelain, each furnished with a relatively'large number of The two parts are firmly connected together by means of the centring pin 9, which is fitted on either side into the central boring.

The lower tube 10 serves for the introduction of the filament leads 20 and 21, whilstthe' body 1, in which there is arranged the double-wound filament 2, is employed as actual heating element. The filament is passed upwards throughone of the passages arranged at the edge, through the next passage downwards, through the, followin passage again upwards, and through the next passage again downwards. The passages may be arranged conveniently in symmetrical fashion. Naturally, it is also possible to employ a larger number of passages, and in this manner to use a greater length of filament. About the body 1 there is firmly placed the metallic cylinder 17, on

the inner side of which there is provided'the highly emissive-coating, which may consist for example of alkaline earth oxide or a mixture of alkaline earth oxides.* The leakage conductance for the cylinder 17 is passed downwards and wound once or several times about the cylinderv 10.

The whole of thiscathode portion is then fitted into a guard tube 11, which may consist of porcelain or any other suitable insulating material. By the passing of the wire 19 about the cylinder 10 any tolerance may be compensated in such fashion that also the cylinder 10 fitscompletely tightly in the tube 11.

The guard tube 11 carries in turna metallic cylinder 12, which is furnished on the upper side with the boring 14, and on which' there may be secured the spiral 15, for example by welding. The one member of this spiral 16 is made to be longer than the other, and projects into a free boring in the body 1. In this manner there is ob-' tained a centring of the spiral 15 in relation to the total cathode arrangement. The cylinder 12 is furnished with a current lead 13 and-particu--- larly if the cathode is to be employed for oscillographic purposes-is maintained at av weaklytials are quite adequate for complete control of the tube from the maximum intensity obtainable down to complete darkness.

For different television circuits it has been found necessary to screen off the heating current (more particularly when using apparatus for connection with house circuits) against the actual emissive surface; An arrangement of this nature with screened filaments is illustrated in Fig. 5. In the latter 1 is the actual heating element havingthe preferably double-wound filaments 2, and 22 a metallic guard cap, which may be raised to a suitable potential with the assistance of the line 23. Naturally the filament leads may also be screened off over their entire length against the current supply to the equipotential surface both within the cathode arrangement as well as outside of the same.

The length of the entire cathode arrangement may be selected for example at approximately 15 mm., and its greatest diameter at somewhat more than 3 mm. The diameter of the elements 1 and 10 mayjamount'for example to 2 mm., the diameter of the spiral 15 to approximately 1.5 mm., and the pitch of the spiral to 0.75 mm. The opening 14 is preferably made extremely small, for exam;- ple 0.5 mm.

' Naturally, the invention is not limited to the form of embodiment set forth. Essential features of the invention are the indirect heating of the actual emissive cathode and the divisioning of the heating element, the provision of an axial space charge grid, and in particular the fact that the single parts are constructed and arranged in such a manner that centring takes emissive material adhering thereto, 4. a control grid, 5' the .anode, 6 the alternating control po-' tential between the emissive coating and the grid, illustrated symbolically as a generator, '1 the point where the generator is taken to earth, and 8 a concentrating shutter, which is preferably grid arranged in means for concentrating, means cylinders.

Agas filled Braun tube comprisingan anode,

' constructed in the manner of a hollow reflector, and may be insulated by the insulating layer 9 against the cathode cylinder. The electrons emitted by the emissive coating 3 are drawn to the anode grid and through the mesh-work of the grid into the inner space thereof, and are sucked out of the anode space by the suctional action of the high-potential anode of the Braun tube, not shown in Fig. 1. It is desirable in accordance with the invention to select the. anode potential of the by way of comparison, for example at approximately 50-5200 volts, in order-that the speed of the electrons is as small as possible in the direction vertical to the cathode ,ray to beproduced.

In Fig. 7, 10 is the cathode, 11 the control grid, 12 the anode, 13 a shutter, 14 a concentration device, "and 15 the anode of the Braun tube.

According to the invention, suitable concentratingmeans of a desired kind may be provided between the shutter and the anode.

The method accordingto the invention, consisting in sucking the electrons necessary to produce the cathode ray from a wattlessecontrolled discharge, preferably vertical to the cathode ray tobe produced; by the suctional action of the anode of the Braun tube, enables in simple fashion the generation of exceedingly intensive image points, theposition ofwhich is completely independent of their intensity.

I claim: v 1. A Braun tube comprising an anode, means for concentrating, means for deflecting the oath-- ode ray, a fluorescent screen, and a cathode arrangement, consisting of an electron emissive surface which is arranged vertically to said an- .ode, a screen furnished with an opening, said screenarranged between said electron emissive surface and said anode, and screening said electron emissive surface against said anode and a parallel to said electron emissive surface in close proximity to said surface. 2. A gas-filled Braun tube comprising an anode, means forconcentrating, means for'deflecting the cathode ray, a fluorescent screen and a cathode arrangement consisting of a metallic tube furnished at its sive coating, a heater element surrounding said tube, a screen furnished with an opening, said screen ar anged between said tube and said anode and creening said electron emissive surface against said anode and a cylindrical grid arranged inside said tube near said emissive coating.

3. A gas filled Braun tube comprising an anode, for deflecting the cathode ray, a fluorescentscree and acathode arrangement consisting of a metallic cylinder, 9. further cylinder consisting of a large-mesh grid arranged inside said metallic cylinder, a metallic ring joining said two cylinders to a double-walled hollow cylinder and arranged between said cylinders and the anode, arid an electron emissive surface, arranged in the space between said-two means for concentrating, means for deflecting the cathode ray, a fluorescent screen, and a cathode arrangement consisting of -a metallic cylinder,

' a further cylinderconsisting of a largemesh grid,

arranged inside said metallic cylinder, a-metallic ring joining said two cylinders to a double-walled hollow cylinder and arranged between, said cylinders and the anode, anda bifllar cathode surprimary path of electrons low' inside with a highly emis-.

. end, said front rounding a part of said grid cylinder with a spacing of not more than 2 mm.

5. A Braun tube comprising an anode, means for concentrating, means for deflecting the oathode ray, a'fluorescent screen, and a cathode arscreening off the space between said two cylinders against said anode.

6. A Braun tube comprising an anode, means for concentrating, means for deflecting the oathode ray, a fluorescent screen, and a cathode arrangement consisting of a metallic cylinder, a front plate closing said metallic cylinder on one end, saidfront plate furnished with an opening, the diameter of which is in the order of 0.5 mm., an insulating cylinder arranged inside said metallic cylinder a further metallic cylinder arranged inside said insulating cylinder, the inner surface of said further metallic cylinder next to said front plate being coated with a highly electron emissive substance, a short insulating cyl-' inder containing a heater element, arranged inside said further metallic cylinder near said highly emissive coating a grid projecting into said further metallic cylinder in asfar as its surface is coated with the highly emissive substance, said grid welded to said front plate and connection means for said heater element and said two metallic cylinders. I

7. A Braun tube comprising an anode, means for concentrating, means for'deflecting the cathode ray, a fluorescent screen and a cathode arrangement, consisting of a metallic cylinder, a

side said further metallic, cylinder near said highly emissive coating, a grid projecting into said further metallic cylinder in as far as its surface is coated with the highlyemissi ve substance; said grid furnished with a holding member, said holding member projecting into a boring of said insulating' element containing. the heater filament and connection. means for said heater filament, the grid and the metallic cylinder coated with the highly emissive substance.

- 8. A Braun tube comprising an anode, means for concentrating, means for deflecting the oathode ray, a fluorescent screen and a cathode arrangement, consisting of a metallic cylinder, a front plate closing said metallic cylinder on one plate furnished with an opening, the diameter of which is in the order of 0.5 mm., an insulating cylinder arranged inside said metallic .cylirider, a further metallic cylinder arranged inside said insulating cylinder, the inner surface of said further metallic cylinder next to said front plate being coated with ajhighly electron emissive substance, a short insulating cylinder containing a heater element, arrangedinside said further metallic cylinder near said. highly emissive coating, a grid projecting into saidfurther metallic cylinder in as far as its surface is coated with, the highly emissive substance, said sulating element containing the heater filament, 1 connection means for said heater filament, the

li'grid and the metallic cylinder-coated with'the highly emissive substance, and a further insulating element arranged inside said insulating tube, said insulating element supporting said connection means. 4

9. A Braun tube comprising an anode, means for concentrating, means for deflecting the cathode ray, a fluorescent screen and a cathode arrangement, consisting ofa metallic cylinder, a front plate closing said metallic cylinder-on one end, said front platefurnished with an opening, the diameter of which is in the order of 0.5 mn'n,

an insulating cylinder arranged inside said metallic cylinder, afurther metallic cylinder arranged inside said insulating cylinder, the inner surface of said further metallic cylinder next to said front plate being coated with a highly electron emissive substance, a short insulating. cylinder containing a heater element, arranged inside said further metallic cylinder near said highly emissive coating, a grid projecting into said further metallic cylinder in as. far as its' surface is coated with the highly emissive substance, said grid furnished with a holding member, said holding member projecting into a boring of said insulating element containing the heater filament and connection means for said heater filament, the grid and the metallic cylinder coated with the highly emissive substance, and a further insulating element arranged inside said insulating tube, said insulating element supporting said con-' ncction means, said insulating element connected with the heater element by means of a pin engaging in central borings of said elements.

10. A Braun tube comprising an anode, means for concentrating, means for deflecting the oathode ray, a fluorescent screen and a cathode arrangement consisting of a metallic cylinder, a front p1ate-closing -said metallic cylinder on one end, said front plate furnished with anopening, the diameter of which is in the order of I 0.5 an insulating cylinder arranged inside said metallic cylinder, 1 a further metallic cylinder arranged inside said insulating cylinder, the inner surface of said further metallic cylinder next to said front plate being coated with ahighly electron emissive substance, a short insulating cylinder containing a heater element, arranged inside said further metallic cylinder near said highly emissive coating, a grid, the pitch of which is in the order .of half of the grid diameter,'projecting into said further metallic cylinder in as far as its surface is coated with the highly emissi've substance, said grid welded to said front plate and connection means for said heater element and said two metallic cylinders.

11. A Braunftube comprising an anode, means for concentrating, means for deflecting the oathode ray, a fluorescent screen, and a cathode arrangement consisting of an electron emissive surface, a screen furnished with an opening, said "screen arranged between said electron emissive surface and said anode; and screening saidelectron emissive surface against said anode'grid arranged'in parallel to said electron emissive surface near said surface, and means for sup ing said gridg j with a control voltage.

- 12. A Braun tube comprising an anode, means for concentrating, means for deflecting the oath-' ode ray, a fluorescent screen, and a cathode arsanode cylinder, 9. grid cylinder surrounding'said' auxiliary anode cylinder, a metallic cylinder, the

inner surface of which is coated with a highly emissive material, surrounding said grid cylinder, a heater element surrounding said metallic cylinder, a'front platefurni'shed withan opening,

closing the entire element and connection means for the heater element, the cathode, the grid and the auxiliary anode.

i i. A Braun tube comprising a plate-shaped anode, means for concentrating, means for defleeting the cathode ray, a fluorescent screen, a cathode arrangement consisting of means for producing and means for controlling electrons said electron producing means including an auxiliary anode,an d a hollow reflector-like shutter arranged between said means and said anode of the Braun tube.

15. A Braun tube comprising ananode, means for concentrating, means for deflecting the oathode ray, a fluorescent screen and a cathode are rangement consisting of an electron emissivesurface, which is arranged vertically to said anode, a screen furnished with an opening, said screen arranged between said electron emissive surface and said anode and screening said electron emissive surface against said anode and a grid arranged in parallel tosaid electronemissive surface in close proximity to said surface, said grid being adapted to be supplied with a bias which is lower than the ionization-voltageof said gas and high enough to produce a space-charge-free space near said emissive surface. I p

16. A Braun tube comprising an anode, means for concentrating,"means for deflecting the. oathode ray, afluorescent screen and. atiathode arrangement consisting of an electron emissive surface which is arranged yertically to said anode,

a screen furnished with an opening, said opening having a diameterof less than two milli metres, said screen arranged between said electron emissive surface and said anode and screenin; said electron emissive surface against said anode and a grid arranged in parallel to said electron emissive surface in close proximity to said surface, said grid being adapted to be supplied with a biaswhich is lower than the ionization-voltage of said gas and high. enough to produce a -space-charge-free space near s'aid emissive surface.

17. A Braun tube comprising an anode; means for concentrating,'means for deflecting the oath-.

ode ray. and a fluorescent screen, a cathode arrangement consisting of 'a metallic cylinder, the inner surface of which is provided with a highly electron emissive coating, a heating element for heating said metallic cylinder, a grid cylinder projecting into said metallic cylinder and a screen screening of! the space between said two cylinders against said anode, said heater element, cathode cylinder and grid cylinder being centered against each other by placing them partly into one another.

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